Programmed-1 frameshifting offers an attractive target for anti-viral agents based on its essential role in the lifecycle of many viruses and its absence in human translation. This proposal focuses on understanding the mechanism for-1 frameshifting by characterizing the structure and the function of a cis-acting, long-distance, frameshift stimulator RNA sequence located in the 3'UTR of barley yellow dwarf virus (BYDV). The use of a long-distance RNA interaction to regulate frameshifting is unique to BYDV frameshifting, and studying this interaction will provide insights into how RNA structures regulate this event. To accomplish this goal, BYDV frameshifting sequences will be analyzed both in vitro and in vivo using a dual luciferase reporter system. The structure of these sequences will be characterized by chemical and nuclease probing, as well as site-directed mutagenesis. Toeprinting assays will be used to determine if RNA sequences induce the ribosome to pause over the shifty side. Completion of these experiments will provide a better understanding of how RNA structures contribute to frameshifting which is important for developing anti-viral agents to alter this event.